Targets Produced in Mass Separators

Abstract

Isotopically enriched nuclear targets are prepared directly in electromagnetic mass separators by allowing the resolved ion species to impinge on a suitable substrate. The calutron, a multi-milliampere mass separator, has been successful in producing ion-implanted targets for nuclear research and in the doping of semiconductors. By using flat magnetic shims, a rotating target holder, and a sliding indexing shutter, multiple targets with uniform implantation have been achieved. The typical accelerating energy for this method is 40 keV, although this can be increased by using multiply charged ions. For production of highly enriched targets from materials in which the desired isotope is of low natural abundance, the 180° Oak Ridge Sector Isotope Separator (ORSIS) has proven particularly successful. This machine, which is an exceptionally high-resolution separator, is interfaced with an on-line computer for surveillance and control. Isotopic enhancement factors of 4 × 105 have been achieved for targets prepared in this machine. Targets are prepared by placing the host material (typically carbon, aluminum, or nickel foils) at the receiver, 1 cm above the normal straight-line beam path. The desired ion species is steered onto the target through an electrostatic beam deflection system, thereby minimizing neutral particle contamination. The energy of an ion at impact, and hence the deposition depth, is controlled by applying a suitable potential (-40 to +40 kV) at the collector. Ion deposition energies from a few electron volts to several hundred kiloelectron volts have been achieved.